Neutrophil extracellular traps: diagnostic and prognostic value in COVID-19

Rationale: An important element of antiviral defense in the pathophysiology of COVID-19 is the innate cell immunity including polymorphonuclear neutrophils prone to netotic transformation. Neutrophils can be not only a marker of acute infection, but, being a source of neutrophil extracellular traps (NET), can play a key role in the development of thrombotic complications leading to acute respiratory insufficiency in COVID-19.Aim: To determine the diagnostic and prognostic value of NET levels in patients with COVID-19.Materials and methods: We monitored NET levels in peripheral blood of 34 patients with COVID-19 (mean age, 67 ± 15.8 years), admitted to MONIKI hospital. The control group consisted of 54 healthy volunteers (mean age, 52 ± 11.5 years). Whole blood samples of 2 pL each were used for the preparation of monolayer smears (Giemsa stain) and calculation of at least 200 cell structures including native intact and transformed neutrophils (MECOS-C2 microscope, Medical computer systems).Results: Patients with COVID-19 had higher NET levels, compared to those in healthy controls: 14.5% (2.9-28.6%) vs. 5.0% (1.8-11.9%, p < 0.0001). The patients who were on non-invasive respiratory support (23.5%) had a NET level of 12% (8.122.3%), whereas those on invasive mechanical ventilation (17.6%) had a 1.5-fold higher NET level of 17.9% (12.3-28.2%) (p < 0.05). In the patients who died (11.8% of the cases), the NET level amounted to 19% (16.5-26%, p < 0.05). Monitoring of blood NET levels was performed in 9 patients from the day of admittance to the day of their transfer to the intensive care unit / discharge / death. It was shown that a decrease of NET levels mirrors an improvement of the patient's clinical condition and efficacy of his/hers treatment. On the opposite, an increase of NET levels can indicate a deterioration and risk of unfavorable course.Conclusion: We have identified some pathophysiological mechanisms in COVID-19, related to the neutrophil compartment. Patients with coronavirus infection are characterized by high NET levels which is at least 3-fold higher than that in healthy volunteers. This indicates an abnormality in immune host defense and development of an inadequate inflammatory response. An increase of NET in whole blood smears of more than 16% can be a criterion of an unfavorable prognosis of the disease course and the risk of death